Orbital welding apparatus is known for: (a) butt welding of tubes using autogenous tungsten inert gas (TIG) welding; such apparatus is exemplified by U.S. Pat. Nos. 2,721,248; 3,035,147; 3,230,340; 3,238,347; 3,395,262; 3,534,199; 3,649,799; 3,780,254; and 3,823,298, and (b) butt welding of tubes using TIG welding with the addition of filler wire as exemplified by U.S. Pat. Nos. 3,409,752 (assigned to the assignee of the present applicant); 3,584,185; 3,780,254; and 3,838,244.
In all cases, in the prior proposals just mentioned, the apparatus is disclosed as having one or more of the following features:
A. OVERALL DIMENSIONS RADIALLY OF THE TUBES TO BE WELDED EQUAL TO SEVERAL TIMES THE DIAMETER OF THE TUBES;
B. A HOUSING WHICH MUST BE OPENED TO ALLOW THE ENTRY OF TUBE TO BE WELDED; THE OVERALL OPENED DIMENSIONS RADIALLY OF THE TUBE IS SEVERAL TIMES (AT LEAST) THE DIAMETER OF THE TUBES WHEN THE HOUSING IS OPENED;
C. SUITABILITY FOR ONLY VERY SMALL DIAMETER TUBES;
D. ABILITY TO PERFORM ONLY AUTOGENOUS WELDS WITHOUT FILLER WIRE OR WITHOUT ANY FEED OF WIRE.
None of the examples of prior proposals for orbital welding apparatus mentioned above shows means for positive feeding of wire into the weld zone using mechanism requiring very small clearance radially of the tube to be welded; for example a clearance such that tube spacing may be as small as about 1 inch for tubes of 3.75 inches outside diameter.
None of the prior art examples is suitable for boiler tube welding in manufacture of boiler tube assemblies; and in the repair of damaged sections of existing boiler tube. In both cases closely adjacent tubes make it imperative that the apparatus have very small clearance requirements and be capable of being offered up to the tubes at one side thereof without the need for opening up a "head" which increases the clearance needed. The feeding of wire for either TIG or metal inert gas (MIG) welding is also essential in boiler tube welding, especially in nuclear power applications.